I have been diabetic, type 1, for 30 years this very month. (I've been reflecting on that today; hence the length of this post.) And I'm at least as healthy now as I have ever been, or possibly more so.
You say your son's blood-sugar "shot up to 14.3", and then you write: "this can happen with moderate exercise, as we know." But you've got things precisely back to front. Any exercise at all will tend to LOWER your son's blood-sugar: the more exercise he takes, the more his blood-sugar will be burnt up.
There is only one kind of blood-sugar reading: the varying effects you have noted will be down to both the insulin (or insulins) your son is taking, and the food he has eaten during the course of the day. (A large amount of cheese during the day, for example, would be sure to push my blood-sugar up high in the evening; a large amount of animal fat is not good for anyone.)
My control is certainly unorthodox. But the orthodoxy is seriously at fault. And in part, but only in part, I believe this is a function of the normal modern diet - diabetic or otherwise. (Doctors tend to eat much the same as everyone else, after all.)
I don't have universal expertise, but I know the effects of the insulin which I take: the effect over time (plotted on a graph) describes a kind of bell-curve. The effect of the Actrapid I take runs out, for me, after around thirteen hours; and the effect of the Novorapid runs out after around eight hours.
If you click on my username, you can see what insulin I take and when I take it: I engineer it so that the respective effects of the two fast-acting insulins both run out together, at midnight. (Naturally, your son's metabolism will have its own characteristics; and his insulin will come with a slip of paper which tells the length of time that it takes effect.)
When I check my blood-sugar at 11.00pm, then - provided I haven't eaten anything during the evening that's only slowly digested - I know (by experience) that my blood-sugar will go down by a further 2mmol/l by 12.00pm, whatever was the reading taken at 11.00pm. And if my blood-sugar is 4mmol/l at 11.00pm, then I know (by experience) that I should eat just one half a slice of the co-op's wholemeal, wheat bread. (The co-op's bread is a regular size, so I know the carbohydrate value is always more-or-less the same.)
I take a very small amount of Insulatard at 11.00pm, which prevents my blood-sugar from rising too much during the course of the night. (I can bump that up a little if my blood-sugar is higher than 6mmol/l at 11.00pm; but I won't bother with the details of that here - your son could just do some vigorous press-ups!) The Insulatard, then, will be the only insulin that's operating within my system during the night. And I can go to sleep knowing that I'm safe.
Regarding my diet, I DON'T HAVE TO WEIGH OR CALCULATE ANYTHING. The obsession with weighing and calculating carbohydrates is what I find most perverse and unreasonable about the orthodox method of control; it's especially unreasonable for children.
I emphasise the importance of eating RYE BREAD most strongly of all. For it's very slowly digested, and so has a moderating effect on the blood-sugar: more than anything else, this prevents me being caught out by a hypo. (I eat rye bread throughout the day, until 4.00pm; and I MUST THEN STOP eating rye, or my blood-sugar is sure to go high later in the evening.)
I have described my dietary regimen in the 'Soapbox - Have Your Say' section of this website: you'll find a fairly lengthy description in the section thread entitled 'Test Strips' - I posted it just a few days ago.
Equally crucially, I test my blood-sugar around 15-20 times per day. But I promise you this is no big deal. (And please, please don't bother with the blasted spring-loaded gadget - one can just use the bare lancet: that's simpler, quicker, gentler, and far more compact to carry around.) Most important in this regard is the availability of the highly economical, visually read testing strips: the only practical ones available are BETACHEK VISUAL. (You can stick the lancet, plus a spare, inside the tube of testing sticks; I use each lancet umpteen times before it starts to get blunt.)
Betachek Visual are on the UK Drug Tariff, but there is currently no UK distributor.
Using a good pair of scissors, and with good eyesight, each of the visually read strips can be cut into five. (The cost to the NHS works out at around 2p per test, which is peanuts alongside the exorbitant cost of electronic testing sticks, with the cumbersome meter - obviously, the electronic sticks cannot be cut with scissors.) Betachek Visual are highly dependable and very accurate for anything below 7mmol/l, which is certainly where my blood-sugar is most of the time.
My blood-sugar often goes slightly low during the course of the day. But SO LONG AS I'VE BEEN EATING RYE (rye bread, or rye flakes, or rye whatever), I promise you that is not a problem. (That's how I keep my HbA1c readings so very low.) But naturally, you will want to be highly cautious about that.
Because of my control, I can expect to have no long-term diabetic complications whatsoever. And if he's careful, your son can expect the same. I wish I'd discovered the beneficial effects of eating rye earlier. Nobody told me about it; I had to discover it for myself.
I think you won't find any medical professional who will endorse what I've recommended here. You will have to try it for yourself. But if you're careful, there will be no risk in trying.
So there are two crucial elements: 1. Eating rye bread (or rye whatever) consistently throughout the morning and the early afternoon (but be careful: not too much - or his blood-sugar will go high in the evening); 2. As much blood-sugar testing as you like, and still more.
Also, I think it's very likely that a change to your son's insulin will be appropriate. And for that you will need to show your doctor what I've written here (prepare yourself for medical protestation), and ask him or her about a change of the insulin regimen.